Configure for C++ too so the testsuite works.

--- expat-2.0.1/configure.in.confcxx
+++ expat-2.0.1/configure.in
@@ -62,6 +62,7 @@ AC_SUBST(LIBAGE)
 
 dnl Checks for programs.
 AC_PROG_CC
+AC_PROG_CXX
 AC_PROG_INSTALL
 
 if test "$GCC" = yes ; then